1. Field of the Invention
The present invention relates to a magnetic recording apparatus such as a floppy disk drive or hard disk drive.
2. Description of the Prior Art
A conventional magnetic recording apparatus will be described. FIG. 4 is a circuit diagram of the writing circuit of a conventional magnetic recording apparatus. The writing circuit amplifies a write signal, by which data is written to a magnetic disk (not shown) such as a floppy disk or hard disk, so as to feed a write current I7 or I8 to a magnetic head 2. In FIG. 4, the two ends of the magnetic head 2 are connected to output terminals 24 and 25 of the writing circuit. The magnetic head 2 has a center tap, which is connected to a supplied voltage Vcc. The write signal is fed in via two input terminals 40 and 41.
The input terminal 40 is connected to the base of an npn-type transistor Q11. The input terminal 41 is connected to the base of an npn-type transistor Q8. The collector of the transistor Q8 is connected to the supplied voltage Vcc. Between the base of the transistor Q8 and the supplied voltage Vcc, a constant current source circuit 42 is connected. The constant current source circuit 42 outputs a current I11 that flows from the supplied voltage Vcc to the base of the transistor Q8. Between the emitter of the transistor Q8 and ground, a resistor R6 is connected. Between the base of the transistor Q8 and ground, a resistor R5 is connected.
The collector of the transistor Q11 is connected to the supplied voltage Vcc. Between the base of the transistor Q11 and the supplied voltage Vcc, a constant current source circuit 43 is connected. The constant current source circuit 43 outputs a current I12 that flows from the supplied voltage Vcc to the base of the transistor Q11. Between the base of the transistor Q11 and ground, a resistor R9 is connected. Between the emitter of the transistor Q11 and ground, a resistor R8 is connected.
The emitter of the transistor Q8 is connected to the base of an npn-type transistor Q9. The emitter of the transistor Q11 is connected to the base of an npn-type transistor Q10. The emitters of the transistors Q9 and Q10 are connected together, and, between this node and ground, a constant current source circuit 23 is connected. The constant current source circuit 23 outputs a constant current I6. The collector of the transistor Q9 is connected to the output terminal 24. The collector of the transistor Q10 is connected to the output terminal 25.
FIG. 5 is a circuit diagram showing the internal configuration of the constant current source circuit 42. The emitter of a pnp-type transistor Q30 is connected through a resistor R20 to the supplied voltage Vcc. The collector of the transistor Q30 is connected to a current source 50. The current source 50 outputs a current I20. The base of the transistor Q30 is connected to the collector of the transistor Q30 and to the base of a pnp-type transistor Q31. Between the bases of the transistors Q30 and Q31 and ground, a parasitic capacitance 51 is present. The emitter of the transistor Q31 is connected through a resistor R21 to the supplied voltage Vcc. From the collector of the transistor Q31, the current I11 is fed out.
This writing circuit is controlled by a controller 7 so as to be either in an active mode in which its data writing operation is permitted or in an inactive mode in which its data writing operation is inhibited. The controller 7 outputs a signal, which is fed to the gates of n-channel MOS transistors Q13 and Q14. The sources of the MOS transistors Q13 and Q14 are each connected to ground. The drain of the MOS transistor Q13 is connected to the input terminal 41, and the drain of the MOS transistor Q14 is connected to the input terminal 40.
In the inactive mode, the controller 7 feeds a high-level signal to the writing circuit. This causes the MOS transistors Q13 and Q14 to be turned on. As a result, the ground voltage is fed to the bases of the transistors Q8 and Q11, which are thus turned off. As a result, the ground voltage is fed to the bases of the transistors Q9 and Q10, which are thus turned off. Consequently, the writing circuit does not operate as a whole, and thus does not feed the write current 17 nor I8 to the magnetic head 2.
By contrast, in the active mode, the controller 7 feeds a low-level signal to the writing circuit. This causes the MOS transistors Q13 and Q14 to be turned off. Consequently, the writing circuit can feed the write current I7 or I8 to the magnetic head 2 in synchronism with the signals fed in via the input terminals 40 and 41.
However, in the circuit shown in FIG. 4, immediately after the supplied voltage Vcc starts being supplied in the magnetic recording apparatus, there is a possibility of a write current being unnecessarily fed to the magnetic head 2 before the entire apparatus becomes ready for writing operation. When electric power starts being supplied, the current source 50 is off, and thus does not output the current I20; however, a current Ic that momentarily flows into the parasitic capacitance 51 induces the base currents of the pnp-type transistors Q30 and Q31, which are thus turned on momentarily, causing the current I11 to flow momentarily. At this moment, if the controller 7 has not yet been started up completely, it cannot feed a high-level signal to the n-channel MOS transistor Q13, and thus cannot make the MOS transistor Q13 absorb the momentary current I11 mentioned just above. This causes a momentary rise in the base voltage of the transistor Q8, which is thus turned on, causing an unnecessary write current to flow via the output terminal 24. This is the reason that there is a possibility of the write current I7 or I8 being unnecessarily fed to the magnetic head 2. Permitting such a flow of the write current I7 or I8 results in noise being written to the magnetic disk (not shown). Accordingly, in a magnetic recording apparatus, it is desirable in the first place that the flow of a write current such as I7 or I8 be inhibited in a transient period such as when electric power has just started being supplied.
An object of the present invention is to provide a magnetic recording apparatus in which, when electric power has just started being supplied, generation of a write current is inhibited to prevent noise.
To achieve the above object, according to the present invention, a magnetic recording apparatus is provided with: a magnetic head for writing data to a magnetic disk; a writing circuit for feeding a write current to the magnetic head; and a temporary shutoff circuit for temporarily deactivating and thereafter activating the writing circuit when electric power starts being supplied.
According to this circuit configuration, when electric power starts being supplied, the temporary shutoff circuit suppresses, for example, the bias voltage output from the writing circuit. Thus, it is possible to prevent writing operation from being unnecessarily performed as a result of a transient current flowing through the magnetic head despite absence of data to be written. In this way, it is possible to prevent noise from being written to the magnetic disk before the bias voltage becomes stable after electric power starts being supplied.